Drilling fluid



United States Patent Delaware No Drawing. Fiied Indy 7, B61, Ser. No. 122,422

Claims. e1. 2szs.s

This invention relates to a water based drilling fluid of the type used in drilling oil, gas, or other deep wells and to a method of reducing the Water loss from drilling fluids.

In the drilling of wells, especially drilling by the rotary method, it is necessary to use a drilling fluid. The principal functions of a drilling fluid are to lubricate and cool the bit and drill stem; carry away cuttings while the drilling is in progress; keep the cuttings in suspension while rilling is shut down; prevent the flow of water, gas, or oil into the well and form an impermeable sheath or filter cake on the walls of the well to reduce water loss and provide support to prevent the collapse of the walls into the well.

The ability of a drilling fluid to accomplish these necessary functions depends primarily upon its physical properties. For example, the fluid must have a viscosity sufficiently high to keep drill cuttings suspended and to carry them from the bottom of the well, but low enough so that it can be easily circulated. In addition, the fluid must have suflicient gel strength to prevent settling of the solids from the fluid when circulation is stopped, but low enough to release the cuttings from the suspension when the fluid is agitated in the settling pits. These problems have been solved by the use of specific clays such as bentonitic clays which impart sufiicient viscosity and gel strength to the fluids. However, the persistent and serious problem of water loss has never been completely solved. By water loss is meant the loss of water by pressure filtration through the filter cake on the walls of the well. Excessive Water loss causes the formation of too thick a filter cake, resulting in the jamming of the drill. In addition, water flowing into the surrounding formations may cause hydration and swelling.

In the past a wide variety of materials has been added to drilling fluids in order to control water loss. Such materials as mica, pectatc pulp, sulfonated rubber, starch and starch derivatives, hydrolyzed polyacrylonitrile, salts of poly(acrylic acid), cellulose and cellulose derivatives, etc., have been used. While such materials can prevent water loss, they often have to be used in such large amounts that they impart other undesirable characteristics to the drilling fluids in which they are incorporated. For example, starch and starch derivatives are subject to bacterial attack and decomposition; hydrolyzed polyacrylonitrile lowers gel strength and increases viscosity beyond the workable ranges, etc.

It has now been found that the water-soluble copolymers prepared from divinyl ether and maleic anhydride in mole ratios of about 1:2 and the water-soluble salts and partial esters thereof can be admixed with various drilling muds to produce improved drilling fluids that exhibit desirable Water loss characteristics even in high calcium systems and good thermal stability and resistance to metal ions without imparting any undesirable characteristics.

Accordingly, this invention relates to a drilling fluid comprising an aqueous suspension of finely divided solid inorganic materials and as a water-1oss preventive an agent selected from the group consisting of divinyl ether-maleic anhydride copolymers, salts of divinyl ether-maleic anhydride copolymers, and water-soluble partial esters of di vinyl ether-maleic anhydride copolymers in an amount suflicient to reduce Water loss but insufiicient to adversely affect viscosity and gel strength.

3,157,599 Patented Nov. 17., 1964 The divinyl ether-maleic anhydride copolymers used as water-loss preventives in this invention are water-solu ble linear copolymers having a reduced specific viscosity (RSV) of from about 0.75 to about 10.0 or even higher and are believed to have a configuration as follows:

The anhydride groups, of course, quickly hydrolyze to free acids in the presence of water.

The term reduced specific viscosity, which is a function of molecular weight, is used herein to designate the /c determined on a 0.1% solution of the copolymer in a l-molar solution of sodium hydroxide measured at a temperature of 25 C.

Exemplary of the salts and partial esters of these copolymers which are useful as water-loss preventives are the water-soluble salts such as the salts of alkali metals, as, for example, sodium, potassium, etc.; ammonium salts; half amide-half ammonium salts; salts of such amines as n-butylamine, t-butylamine, methylamine, ethylarnine, dimethylamine, trimethylamine, diethylamine, triethylamine, etc.; mixed salts containing ammonia and a low molecular weight primary or secondary amine; the water-soluble partial esters such as those of methanol, ethanol, butanol, etc.; and the water-soluble partial esters of alkanol amines such as those of methanolamine, ethanolamine, isopropanolamine, diethanolamine, 2-amino-2-methyl-l-propanol, Z-amino-l-butanol, 2(dimethylamino)ethanol, etc. The amine groups of these alkanol amine esters can and often do form salts with the free carboxylic acid groups.

The partial esters of the copolymers can readily be prepared by various methods, as, for example, by refluxing a slurry or solution of the copolymer with the theoretical amount of alcohol.

In general, when preparing the salt, sufiicient salt-forming component is added to the copolymer to completely hydrolyze the anhydride groups. However, since the copolymer itself is an eflicient water-loss preventive, less than a stoichiometric amount of a salt-forming component can be used.

In preparing the drilling fluids of this invention, the copolymer water-loss preventive can be added by various methods. For example, the dry, finely divided solid can be mixed with a minimum amount of water to form a paste which can then be added to the mud. If a salt is desired, the required amount of salt-forming component can be added to the paste first and the preformed salt then added to the mud or the salt can be formed in situ.

The amount of the copolymer necessary to prevent water loss depends upon many factors, as, for example, the molecular Weight of the copolymer, the nature of the drilling mud to which it is added, etc., and can best be determined by the driller in view of the specific task at hand. While the amount will vary greatly depending upon different factors, it will generally be within the range of from about 0.2% to about 2.0% by Weight based on the weight of the drilling mud.

The water-loss preventives of this invention function equally well in the presence of the different mud types, such as fresh Water mud, salt water mud, gypsum mud, etc., normally encountered in drilling.

The copolymers used in the preparation of the drilling fluids of this invention are produced by copolymerizing divinyl ether and maleic anhydride in an aromatic diluent PREPARATION OF A TYPICAL DlVINYL ETHER- MALEIC ANHYDRIDE COPQLYMER (1) Stormer viscositypage 6 (2) Apparent viscosity (low-speed reading from direct indicating viscometer)page 7 (3) Plastic viscosity (high-speed minus lw-speed read ing from direct indicating viscometer)--page 7 A polymerization vessel was charged with 9.8 parts (4) Initial gel strength-page 6 of maleic anhydride at a temperature of 20 C., flushed (5) Ten-minute gel strengthpage 6 with nitrogen, and then charged with 66 parts of nitrogen- (6) W t lgss pages 9 nd sparged benzene. After dissolution of the maleic anhy- (7) Filter cake thickness-pages 9 and 10 dride, 3.46 parts of distilled diviiiyl ether, 0.0048 part 10 I gaseous oxygen, and 1.08 parts of bromotrichlorometh- A description of someof thesetests (Nos. 1, 4, 5, 6, and ane were added. Then with vigorous agitation there was 7) may also be found in Principles of Drilling Mud Conadded 0.029 part of triethylborine, (C H B, as a 1 M tiol," 8th Edition of the Industrial and Business Training solution in n-lieptane. Within 10 seconds copolymeriza- Bureau, Division of Extension, University of Texas, Austion started and the solution became cloudy and then tin, Texas (1951). gelatinous. After about hours the reaction stopped Emmple 1 and the reaction mixture was repeatedly extracted with benzene and then dried under vacuum. The resulting di- Drilling fiulds P P with re typss of l vinyl ethepmalsic anhydride copolymer was a White ing muds and the sodium salt of the divinyl ether-male c powder h i an RSV f 3 and represented a conver 20 anhydride copolyiner described above. The formulas (in Sign of 85% The divinyl ether and maleic anhydride weight percentages) of the drilling muds used were as were present in the copolymer in the molar ratio of 1:2. follows:

It will be understood that by conducting the copolymerization under various reaction conditions in the presence of diiferent free-radical initiators and in the presence a g K3 or absence of chain transfer agents (i.e., CCl BrCCl Mud etc.) copolymers of various RSVs, i.e., various molecular weights, can be prepared. Texas Qlay It is pointed out that there are no general optimum g i l aiiuin Slllfat8 characteristics which can be used to describe all drilling Calcium Sulfate fluids nor is there a universal drilling fluid. The char- S i Carbonate odium Chloride acteristics of drilling fluids used in different locations with Water diflerent muds are by necessity drastically different. For example, the so-called Gulf Coast muds require the use of a drilling fluid of low viscosity (about 15-20 cps), The drilling fluids tested were prepared by first making minimum gel strength, and very high Water loss prevena paste of the copolymer with water, then adding aqueous tion (preferably less than 6 ml. in 30 minutes). The sosodium hydroxide until a gel formed. The resulting gel called West Texas muds, on the other hand, require the was then added to one of the above muds with agitation use of a drilling fluid of high viscosity (about 80400 in the amount required to make a drilling fluid of the cps.), maximum gel strength, slight Water loss prevention desired weight percentage. In all cases the drilling fluids (preferably less than 30 ml. in 30 minutes), and high salt were aged overnight and adjusted to a pH of 11. To tolerance. show the elfect of high temperature encountered in deep- The following examples present the preparation of well drilling, some of the fluids were subjected to a 16- typical drilling fluids for purposes of illustration, parts hour aging period at a temperature of 150 C. prior to and percentages being by Weight unless otherwise testing. indicated. The specific drilling fluid used, weight percentage of The following standard tests mentioned in the examples co olyrner salt in the drilling fluid, and the Stormer visare described in Standard Field Procedure for Testing cosity, initial gel strength, IO-rninute gel strength, water Drilling Fuids, 4th edition of The American Petroleum loss, and filter cake thickness of each are tabulated in Institute (May 1957) on the pages indicated. Table I.

TABLE I Weight Initial lo-hiinute Water Filter Percent Stormer Gel Gel Loss, Cake Drilling Fluid ofCopol- Viscosity, Strength, Strength, ml. 1:130 Thickymer cps. g. g. minutes ness, Added inches Fresh Water Mud 0 51 80 80 76 0. 462 0 25 40 3 4 11.6 0. 062 0 so 03 3 4 5.0 0. 035 0. 112 7 s 4. 1 0. 0 14 Fresh Water Mud subjected to heat treatment. 0 51 8O 76 0. 462 0. 25 as 4 4 12. 4 0. 078 0.50 28 s a 5.1 0. 078 0.75 24 3 4 3.8 0. 040

Gypsum Mud O 13 1O 15 68 0. 344 0. 25 43 4 5 10. 4 0. 004 0. 50 as 5 6 5.8 0. 039 0. 75 15 15 4. s 0. 030

Gy sum Mud subjected to heat treatment 0 13 10 15 68 0. 344 0. 25 43 4 5 i4. 5 0. 101 0. s0 24 4 5 7.4 0.110 0.75 28 4 4 5.4 0. 045

' alt Water Mud 0 16 10 10 172 0. 780 1.0 20 4 4 5.4 0.048 1.5 26 5 5 2.6 0. 03s

It can be seen from the above table that the addition of small amounts of the copolymer salt drastically reduced water loss and filter cake buildup without adversely affecting the viscosity or gel strength.

Example 2 Drilling fluids were prepared (as described in Example 1) from the fresh water mud (described in Example 1) and the sodium salt of a divinyl ether-maleic anhydride copolymer having an RSV of 1.4.

The weight percentage of copolymer salt in the drilling fluid and the Stormer viscosity, initial gel strength, 10-minute gel strength, water loss, and filter cake thickness of each fluid are tabulated below.

Weight percent of copolymer added 0. 5 Stormcr Viscosity, cps 51 47 Initial Gel Strength, g 8O 4 Ill-Minute Gel Strength, g SO 4 Water Loss, ml. in 30 minutes... 76 6. 5 Filter Cake Thickness, inches 0. 462 0. 036

Example 3 Drilling fluids were prepared (as described in Example 1) from the fresh water mud and the gypsum mud (described in Example 1) and the sodium salt of a divinyl ether-maleic anhydride copolymer having an RSV of 0.9.

The specific drilling fluid used, weight percentage of copolymer salt in the drilling fluid, and the Stormer viscosity, initial gel strength, 10-minute gel strength, and water loss of each are tabulated in Table 11.

A half amide-half ammonium salt of a divinyl ether maleic anhydride copolymer having an RSV of 1.4 was prepared as follows: To 500 parts of benzene were added 50 parts of divinyl ether-maleic anhydride copolymer. Gaseous ammonia was bubbled through the resulting slurry for 1.5 hours during which time the temperature increased from C. to 50 C. The resulting salt was filtered, washed with benzene, and dried. From nitrogen and oxygen analyses it was calculated that 68.5% of the starting maleic anhydride units were converted to ammonium maleamate units.

Drilling fluids were prepared by adding the dry half amide-half ammonium salt of the copolymer to a fresh water, low-solids mud containing 3.5% attapulgite clay.

The weight percentage of the copolymer salt in the drilling fluid and the apparent viscosity, plastic viscosity, and water loss are tabulated below:

Salt water drilling fluids were prepared from a lowsolids salt water mud containing 3.5% attapulgite clay and the half amide-half ammonium salt of the divinyl ether-malcie anhydride copolymer described in Example 4.

The Weight percentage of the copolymer salt added to the drilling fluid, the weight percentage of sodium chloride in the drilling fluid, and the apparent viscosity, plastic viscosity, and water loss are tabulated below.

A tert-butylamine salt ot a divinyl ether-maleic anhydride copolymer having an RSV of 1.5 was prepared as follows: To 500 parts of benzene were added 50 parts of divinyl ether-maleic anhydride copolymer and an mount of tert-butylamine equal to 4 moles of amine per base mole of copolymer (a base mole of copolymer is one containing two anhydride units). The resulting slurry was refluxed for 5 hours, cooled, filtered, washed with benzene, and dried. From a nitrogen analysis it was calculated that 44% of the starting maleic anhydride units were converted.

Drilling fluids were prepared by adding the dry salt to a low-solids gypsum mud containing 3.5% attapulgite clay and 0.6% calcium sulfate.

The weight percentage of the copolymer salt in the drilling fluid and the apparent viscosity, plastic viscosity, and water loss are tabulated below:

Example 7 A monoester-monoamine derivative of a divinyl ethermaleic anhydride copolymer having an RSV of 1.5 was prepared as follows: To 500 parts of benzene were added 50 parts of divinyl ether-maleic anhydride copolymer and an amount of dimethylaminoethanol, (CH NCH CH OH, equivalent to 7. moles of alkanolamine per base mole of copolymer. The resulting slurry was refluxed for 5 hours, cooled, filtered, washed with benzene, and dried. From a nitrogen analysis it was calculated that 73% of the starting maleic anhydride units were converted. An infrared spectrum of the product showed the presence of both ester and amine salt groups.

Drilling fluids were prepared by adding the dry ester to the low-solids, 26% sodium chloride-containing mud described in Example 5.

The weight percentage of copolymer ester in the drilling fluid and the apparent viscosity, plastic viscosity, and Water loss are tabulated below:

Weight Percent of COWlylllQl Added 0 1. 2 Apparent Viscosity, c 11 27 Plastic Viscosity, cps 3 15 Water Loss, H11. in 30 minutes 10 Example 8 TABLE III Weight Percent Water Drilling Fluid of Water- Loss,

Loss Premi, in 30 ventivo minutes Added Fresh water mud V 7 containing;

Sodium carboxymethylecllulose 0. 25 23, 9 The sodium salt of polymerylic aei'l) 0,25 19, 2 The sodium salt of divinyl eth r-malcic anhydride eopolymer I 0 25 11.6 Sodium carboxymethyleellulo 0. 50 17.4 The sodium salt oi poly (ear 0 acid) 0. 50 9, 0 The sodium salt of ti yl ether-maleie anhydride copolymerieu 0.50 0 Fresh water mud, heat treated I .7 0 7 and containing.

Sodium carboxymethyleellulose 0. to 15,9, he sodium salt of poly(aeryl1c aeld) Ov 50 I0. 0 The sodium salt of divinyl ctlier-maleic anhydride copolymeL- A. 0. a0 5.1 Gypsum mud .7 0 as,

containing:

Sodium corboxymethylcclluloseI H 0.25 12.9 The sodium salt of poly acrylie acid) 0. 25 12, 2 The sodium salt of (iiviuyl other anhydride copolymer A 0v 25 1o, 4 Sodium carboxymethylecllulosa H O. 50 9. 0 The sodium salt of poly(serylie acid), is U. 8i 6 The sodium salt oi divinyl ether-maleic anhydride co polymer i. is 0. .50 5, 8 Gypsum mud, heat treated I 0 g and containing:

Sodium carhoxymethyleollulose H 0.25 17. 3 The sodium salt of poly acrylie acid) 0 0.25 18.1 The sodium salt of di\ iyl ether-maieio unhydririe copolymer .7 0. 25 14 5 Sodium carboxyinethyloellulose .w i 0. 50 12 The sodium salt of pelynrerylie acid). I (J. 50 13 The sodium salt of divinyl ether lelc anhydiirio copolymermfihhfl r 0.50 7 4 Salt water mud H 0 172 containing:

The sodium salt of polyme lie acid). 1.0 48 Sodium earboxymethyleellurose H 1.0 7 5 The sodium salt of divinyl etlier-nia eio anhydride copolymer 1.0 5, 4

X Subjected to a 16-hour aging period at a temperature of 150 0. prior to testing.

What I claim and desire to protect by Letters Patent is:

1. A drilling fluid comprising an aqueous suspension of finely divided, solid, inorganic material and as a waterloss preventive an agent prepared from divinyl ether and maleic anhydride in the molar ratio of about 1:2 and selected from the group consisting of divinyl ether'maleic anhydride copolymers, alkali metal, ammonium, half amide-half ammonium, and alkyl amine salts of divinyl ether-maleic anhydride copolymers, water-soluble partial esters of lower monohydroxy aliphatic alcohols with divinyl ether-maleic anhydride copolymers and water-soluble partial esters of alkanol amines with divinyl ethermaleic anhydride copolymers.

2. The composition of claim 1 wherein the water-loss preventive is a sodium salt of a divinyl ether-maleie anhydride copolymer.

3. The composition of claim 1 wherein the water-loss preventive is the half amine-half ammonia salt of a divinyl ether-maleic anhydride copolymer.

4. The composition of claim 1 whereni the water-loss preventive is the tert-butylamine salt of a divinyl ethermaleic anhydride copolymer.

5. The composition of claim 1 wherein the water-loss preventive is the dimethylaminoethanol derivative of a divinyl ether-maleic anhydride copolymer.

6. In a process for drilling a well wherein there is circulated in the well an aqueous suspension of finely divided solid inorganic material, the method of forming a filter cake on the Wall of said well to decrease the loss of fluid from said aqueous suspension contained therein into surrounding earthen formations which comprises incorporating in said aqueous suspension a water-loss preventive prepared from divinyl ether and maleic anhydride in the molar ratio of about 1:2 and selected from the group consisting of divinyl ether-maleic anhydride copolymers, alkali metal, ammonium, half amide-half ammonium and alkyl amine salts of divinyl ether-maleic anhydride copolymers, water-soluble partial esters of lower monohydroxy aliphatic alcohols with divinyl ethermaleic anhydride copolymers and Water-soluble partial esters of alkanol amine with clivinyl ether-maleic anhydride copolymers and contacting said wall of said well with the resulting aqueous suspension to form said filter cake thereon.

7. The method of claim 6 wherein the later-loss preventive is the sodium salt of a divinyl ether-maleic anhydride copolymer.

8. The method of claim 6 wherein the water-loss preventive is the half amide-half ammonium salt of a divinyl ethcr-maleic anhydride copolymer.

9. The method of claim 6 wherein the water-loss preventive is the tert-butylamine salt of a divinyl ethermalelc anhydride copolymer.

10. The method of claim 6 wherein the water-loss preventive is the dimethylaminoethanol derivative of a divinyl ether-maleic anhydride copolymer.

References Cited by the Examiner UNITED STATES PATENTS 2,647,886 8/53 Seymour 252- 2,718,497 9/55 Oldharn et al. 252-8.5 3,085,077 4/63 Floyd 260-29] FOREIGN PATENTS 553,011 2/58 Canada.

JULIUS GREENWALD, Primary Examiner. 

1. A DRILLING FLUID COMPRISING AN AQUEOUS SUSPENSION OF FINELY DIVIDED, SOLID, INORGANIC MATERIAL AND AS A WATERLOSS PREVENTIVE AN AGENT PREPARED FROM DIVINYL ETHER AND MALEIC ANHYDRIDE IN THE MOLAR RATIO OF ABOUT 1:2 AND SELECTED FROM THE GROUP CONSISTING OF DIVINYL ETHER-MALEIC ANHYDRIDE COPOLYMERS, ALKALI METAL, AMMONIUM, HALF ANIDE-HALF AMMONIUM, AND ALKYL AMINE SALTS OF DIVINYL ETHER-MALEIC ANHYDRIDE COPOLYMERS, WATER-SOLUBLE PARTIAL ESTERS OF LOWER MONOHYDROXY ALIPHATIC ALCOHOLS WITH DIVINYL ETHER-MALEIC ANHYDRIDE COPOLYMERS AND WATER-SOLUBLE PARTIAL ESTERS OF ALKANOL AMINES WITH DIVINYL ETHERMALEIC ANHYDRIDE COPOLYMERS. 